This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 24 |
| 3 | 168 |
| 4 | 1056 |
| 5 | 0 |
| 6 | -229824 |
| 7 | -7233408 |
| 8 | -162860544 |
| 9 | -2573835264 |
| 10 | 0 |
| 11 | 2333140153344 |
| 12 | 131053381595136 |
| 13 | 4948323499671552 |
| 14 | 124773727026364416 |
| 15 | 0 |
| 16 | -256422032696998232064 |
| 17 | -20710128948965418074112 |
| 18 | -1096668276542495972130816 |
| 19 | -37948699305215165278715904 |
| 20 | 0 |